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| United States Patent |
5,108,651
|
|
Terashima
, et al.
|
April 28, 1992
|
Ferroelectric liquid crystal composition
Abstract
A ferroelectric liquid crystal composition having a negative large
dielectric anisotropy value, AC stabilizing effect at low voltages and yet
high-speed response properties, and a light switching element using the
composition are provided, which composition comprises at least two
components at least one of which is a compound expressed by the formula
##STR1##
wherein R.sup.3 and R.sup.4 each represent the same or different linear or
branched alkyl group of 1-18C and l is 1 or 2, and having a negative
dielectric anisotropy value.
A preferred embodiment of the above composition contains at least three
components A, B and C, one of which is the above compound of the formula
(A) and components B and C of which are each selected from a group of
specified compounds, and the respective proportions of components A, B and
C being 5-50 weight %, 20-70 weight % and 5-40 weight % based on the total
weight of the three, respectively.
| Inventors:
|
Terashima; Kanetsugu (Kanagawa, JP);
Ichihashi; Mitsuyoshi (Kanagawa, JP);
Kikuchi; Makoto (Kanagawa, JP);
Takeshita; Fusayuki (Kanagawa, JP);
Furukawa; Kenji (Kanagawa, JP)
|
| Assignee:
|
Chisso Corporation (Ohsaka, JP)
|
| Appl. No.:
|
285521 |
| Filed:
|
December 16, 1988 |
Foreign Application Priority Data
| Dec 25, 1987[JP] | 62-328717 |
| Current U.S. Class: |
252/299.61; 252/299.01; 252/299.63; 252/299.65; 252/299.66 |
| Intern'l Class: |
C09K 019/34; C09K 019/52; C09K 019/30; C09K 019/12 |
| Field of Search: |
252/299.61,299.63,299.65,299.66,299.01
|
References Cited
U.S. Patent Documents
| 4368135 | Jan., 1983 | Osman | 252/299.
|
| 4490015 | Dec., 1984 | Kawarada et al. | 252/299.
|
| 4780240 | Oct., 1988 | Emoto et al. | 252/299.
|
| 4780241 | Oct., 1988 | Furukawa et al. | 252/299.
|
| 4784792 | Nov., 1988 | Inoue et al. | 252/299.
|
| 4886620 | Dec., 1989 | Hopf et al. | 252/299.
|
Primary Examiner: Maples; John S.
Assistant Examiner: Tucker; Philip
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Claims
What we claim is:
1. A ferroelectric liquid crystal composition which comprises at least the
following three components A, B and C in proportions of 5 to 40% by weight
of component, A, 20 to 70% by weight of component B and 5 to 40% by weight
of component C, and having a negative dielectric anisotropy value:
component A being a compound expressed by the formula
##STR66##
wherein R.sup.3 and R.sup.4 each represent the same or different linear
or branched chain alkyl group each of 1 to 18 carbon atoms, and l
represents 1 or 2;
component B being at least one member selected from the group consisting of
a compound expressed by the formula
##STR67##
wherein R.sup.5 and R.sup.6 each represent the same or different linear
or branched chain alkyl group or alkoxy group each of 1 to 18 carbon
atoms,
a compound expressed by the formula
##STR68##
wherein R.sup.7 and R.sup.8 each represent the same or different linear
or branched chain alkyl group or alkoxy group each of 1 to 18 carbon
atoms,
a compound expressed by the formula
##STR69##
wherein R.sup.9 and R.sup.10 each represent the same or different linear
or branched chain alkyl group or alkoxy group each of 1 to 18 carbon
atoms, and
a compound expressed by the formula
##STR70##
wherein R.sup.11 represents a linear or branched chain alkyl group or
alkoxy group each of 1 to 18 carbon atoms, Z represents a direct bond or
--O--, k represents 0 to 10, and (.+-.) indicates racemic compounds; and
component C being at least one member selected from the group consisting of
a compound expressed by the formula
##STR71##
wherein R.sup.12 represents a linear or branched chain alkyl group or
alkoxy group each of 1 to 18 carbon atoms, R.sup.13 represents a linear or
branched chain alkyl group of 2 to 18 carbon atoms, W represents --H, --F
or --CN, and * indicates an asymmetric carbon atoms,
a compound expressed by the formula
##STR72##
wherein R.sup.14 represents a linear or branched chain alkyl group or
alkoxy group each of 1 to 18 carbon atoms, R.sup.15 represents a linear or
branched chain alkyl group of 2 to 18 carbon atoms, V represents --H, --F
or --CN, and * indicates an asymmetric carbon atoms,
a compound expressed by the formula
##STR73##
wherein R.sup.16 represents a linear or branched chain alkyl group or
alkoxy group each of 1 to 18 carbon atoms, R.sup.17 represents an alkyl
group of 1 to 18 carbon atoms, and * indicates an asymmetric carbon atom,
and
a compound expressed by the formula
##STR74##
wherein R.sup.18 represents a linear or branched chain alkyl group or
alkoxy group each of 1 to 18 carbon atoms, R.sup.19 represents a linear or
branched chain alkyl group of 2 to 18 carbon atoms or an alkoxy group of 1
to 18 carbon atoms, and * indicates an asymmetric carbon atom.
2. A ferroelectric liquid crystal composition according to claim 1, wherein
R.sup.3 and R.sup.4 in the formula (A) each represent a linear alkyl group
of 3 to 7 carbon atoms.
3. A light switching element using a ferroelectric liquid crystal
composition according to claim 1, wherein AC stabilizing effect is
utilized.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a ferroelectric liquid crystal composition. More
particularly it relates to a ferroelectric liquid crystal composition
having a negative dielectric anisotropy comprising an achiral compound
having a negative dielectric anisotropy and a light switching element
using the same.
2. Description of the Related Art
In recent years, liquid crystal display has come to be broadly employed for
display elements, utilizing the specific features thereof, such as light
weight, small power consumption, etc. However, most of these display
elements utilize TN display mode using liquid crystal materials having a
nematic phase; hence in the application fields where high multiplexity is
required, the response time is still slow so that there has been a need
for improving the elements.
In such present status, a display mode which has recently been noted is the
one proposed by N. A. Clark and S. T. Lagerwall, i.e. a display mode
utilizing a light switching phenomenon of ferroelectric liquid crystals
(see Applied Physics, Letters, Vol. 36, p. 899 (1980)). The presence of
ferroelectric liquid crystals has been stated by R. B. Meyer for the first
time (see Journal de Physique, vol. 36, p. 69 (1975)), and from the
viewpoint of classification of liquid crystals, the ferroelectric liquid
crystals belong to chiral smectic C phase, chiral smectic I phase, chiral
smectic F phase, chiral smectic G phase, chiral smectic H phase, chiral
smectic J phase and chiral smectic K phase (hereinafter abbreviated to SC*
phase, SI* phase, SF* phase, SG* phase, SH* phase, SJ* phase and SK*
phase, respectively).
When the light switching effect of ferroelectric liquid crystals is applied
to display elements, there are two superior specific features as compared
with TN display mode. The first specific feature is that the response is
made at a very high rate and the response time is 1/100 or less that of TN
display mode elements. The second specific feature is that there is a
memory effect, which makes multiplex drive easy coupled with the
above-mentioned high-speed properties.
In order for display elements using ferroelectric liquid crystals to have
memory properties, two methods are considered. One of these is a method
proposed by N. A. Clark et al wherein memory properties are developed by
reducing the cell thickness (d) down to a thickness of the helical pitch
(p) or less to thereby undo the helix (Applied Physics, Letters, vol. 36,
p. 899 (1980)) and the other is a method found by Le Piesant wherein
memory properties are developed by utilizing AC stabilizing effect (Paris
Liquid Crystal Conference, p. 217 (1984)). The word AC means alternate
current hereinafter.
Most current ferroelectric liquid crystal materials have short helical
pitches (1 to 3 .mu.m); hence in order to develop memory properties by
reduction in the thickness of the cell, proposed by N. A. Clark et al, it
is necessary to retain the cell thickness at about 1 to 3 .mu.m, but from
the viewpoint of the current cell preparation technique, there is a
problem that the retention is difficult in the aspects of cost and yield.
On the other hand, the method found by Le Piesant wherein memory
properties are developed utilizing AC stabilizing effect is effective only
for ferroelectric liquid crystal materials having a negative dielectric
anisotropy (.DELTA..epsilon.), but even in the case of thick cells (5 to 7
.mu.m), it is possible to develop memory properties; thus the current cell
preparation technique is utilizable and hence the method is very
practical.
The AC stabilizing effect is due to a mode utilizing the following fact:
Spontaneous polarization (Ps) results from an impressed electric field in
the case where low frequency is applied to ferroelectric liquid crystals,
whereas spontaneous polarization does not follow in the case of high
frequency; as a result, normal dielectric anisotropy becomes effective and
hence if the dielectric anisotropy value is negative (.DELTA..epsilon.<0)
liquid crystal molecules are compelled to be in a parallel state to the
substrate. Thus, memory properties are developed even in the case of a
thick cell. A matrix display utilizing this AC stabilizing effect has been
actually reported by Jeary in 1985 for the first time (SID'85, Digest, p.
128 (1985)), but thereafter almost no report has been issued. The main
reason for so few reported examples is that there are so few ferroelectric
liquid crystal materials having a negative dielectric anisotropy value.
Further, according to Jeary's report, a voltage of about 40 V is required
for developing memory properties by utilizing AC stabilizing effect, but
when usual IC drive voltage range is taken into account, it is desired
that AC stabilizing effect be developed at a far lower voltage (25 V or
less). As to AC stabilizing effect, the more the negative dielectric
anisotropy value, the lower the voltage of the effect developed; hence
appearance of ferroelectric liquid crystal materials having a negative
larger dielectric anisotropy value has been earnestly desired. Further,
the response time of ferroelectric liquid crystal materials reported by
Jeary et al is several msecs, that is, the response time is still slow in
the aspect of practical use; hence appearance of ferroelectric liquid
crystals having a negative dielectric anisotropy value and also high-speed
response properties has been desired.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a ferroelectric
liquid crystal composition having a negative large dielectric anisotropy
value, an AC stabilizing effect at lower voltages and yet high-speed
response properties.
A second object of the present invention is to provide a light switching
element using the abovementioned liquid crystal composition.
The present inventors have conducted extensive research in order to solve
the above-mentioned problems, and as a result, have found that when
certain liquid crystal compounds are combined together as shown below, a
ferroelectric liquid crystal composition having a negative large
dielectric anisotropy value and yet high-speed response properties is
obtained, and have achieved the present invention.
The present invention in a first aspect resides in
a ferroelectric liquid crystal composition having a negative dielectric
anisotropy value and comprising at least two components at least one of
which is a compound expressed by the formula
##STR2##
wherein R.sup.3 and R.sup.4 each represent the same or different linear or
branched chain alkyl group each of 1 to 18 carbon atoms and l represents 1
or 2,
having a negative dielectric anisotropy value and
being contained in the composition in an amount of 5% by weight or more. As
a preferable embodiment of the above-mentioned liquid crystal composition,
there is provided
a ferroelectric liquid crystal composition having a negative dielectric
anisotropy value and comprising at least the following three components A,
B and C in proportions of 5 to 40% by weight of component A, 20 to 70% by
weight of component B and 5 to 40% by weight of component C:
component A being a compound expressed by the above-mentioned formula (A);
component B being at least one member of a compound expressed by the
formula
##STR3##
wherein R.sup.5 and R.sup.6 each represent the same or different linear or
branched chain alkyl group or alkoxy group each of 1 to 18 carbon atoms,
a compound expressed by the formula
##STR4##
wherein R.sup.7 and R.sup.8 each represent the same or different linear or
branched chain alkyl group or alkoxy group each of 1 to 18 carbon atoms,
a compound expressed by the formula
##STR5##
wherein R.sup.9 and R.sup.10 each represent the same or different linear
or branched chain alkyl group or alkoxy group each of 1 to 18 carbon
atoms, or
a compound expressed by the formula
##STR6##
wherein R.sup.11 represents a linear or branched chain alkyl group or
alkoxy group each of 1 to 18 carbon atoms, Z represents a direct bond or
--O--, k represents 0 to 10 and (.+-.) indicates racemic compounds; and
component C being at least one member of a compound expressed by the
formula
##STR7##
wherein R.sup.12 represents a linear or branched chain alkyl group or
alkoxy group each of 1 to 18 carbon atoms, R.sup.13 represents a linear or
branched chain alkyl group of 2 to 18 carbon atoms, W represents --H, --F
or --CN and * indicates an asymmetric carbon atom,
a compound expressed by the formula
##STR8##
wherein R.sup.14 represents a linear or branched chain alkyl group or
alkoxy group each of 1 to 18 carbon atoms, R.sup.15 represents a linear or
branched chain alkyl group of 2 to 18 carbon atoms, V represents --H, --F
or --CN and * indicates an asymmetric carbon atom,
a compound expressed by the formula
##STR9##
wherein R.sup.16 represents a linear or branched chain alkyl group or
alkoxy group each of 1 to 18 carbon atoms, R.sup.17 represents an alkyl
group of 1 to 18 carbon atoms and * indicates an asymmetric carbon atom,
or
a compound expressed by the formula
##STR10##
wherein R.sup.18 represents a linear or branched chain alkyl group or
alkoxy group each of 1 to 18 carbon atoms, R.sup.19 represents a linear or
branched chain alkyl group of 2 to 18 carbon atoms or an alkoxy group of 1
to 18 carbon atoms and * indicates an asymmetric carbon atom.
The present invention in a second aspect resides in
a light switching element comprising the above-mentioned ferroelectric
liquid crystal composition having a negative dielectric anisotropy value,
and utilizing AC stabilizing effect.
DESCRIPTION OF THE DRAWINGS
FIG. 1 shows graphs illustrating AC stabilizing effect of the ferroelectric
liquid crystal composition of the present invention wherein 1(a) shows a
graph illustrating the wave of impressed voltage, 1(b) shows a graph
illustrating the memory properties of a ferroelectric liquid crystal
composition composed mainly of components B and C but containing no
component A; and 1(c) shows a graph illustrating memory properties of a
ferroelectric liquid crystal composition having component A added to the
above-mentioned composition.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Since the compound expressed by the formula (A) in the present invention
has a large dipole moment (represented by CN) in the perpendicular
direction to the molecules, it has a very notable characteristic. A patent
application for this compound, which has been laid open, has previously
been applied for by the present applicants (e.g. Japanese patent
application laid-open Nos. Sho 55-66556/1980, Sho 55-102550/1980 and Sho
59-10557/1984).
The compound expressed by the formula (A) exhibits a nematic phase or
smectic A phase and exhibits no SC phase, but it has a negative dielectric
anisotropy value as very large as -20 to -25; hence it plays an important
role of causing AC stabilizing effect to develop at low voltages in the
ferroelectric liquid crystal composition of the present invention.
Representative examples of the compound expressed by the formula (A) are
shown in the following Tables 1 and 2, Table 1 showing compounds of the
formula (A) wherein l=1 and expressed by the formula
##STR11##
and Table 2 showing those wherein l=2 and expressed by the formula
TABLE 1
______________________________________
R.sup.3 R.sup.4 R.sup.3 R.sup.4
______________________________________
C.sub.3 H.sub.7 --
--C.sub.5 H.sub.11
C.sub.5 H.sub.11 --
--C.sub.6 H.sub.13
" --C.sub.6 H.sub.13
" --C.sub.7 H.sub.15
C.sub.4 H.sub.9 --
--C.sub.3 H.sub.7
C.sub.6 H.sub.13 --
--C.sub.4 H.sub.9
" --C.sub.4 H.sub.9
" --C.sub.5 H.sub.11
" --C.sub.5 H.sub.11
" --C.sub.6 H.sub.13
" --C.sub.6 H.sub.13
" --C.sub.7 H.sub.15
" --C.sub.7 H.sub.15
C.sub.7 H.sub.15 --
--C.sub.3 H.sub.7
.sup. C.sub.5 H.sub.11 --
--C.sub.3 H.sub.7
" --C.sub.4 H.sub.9
" --C.sub.4 H.sub.9
" --C.sub.5 H.sub.11
" --C.sub.5 H.sub.11
" --C.sub.6 H.sub.13
______________________________________
TABLE 2
______________________________________
R.sup.3 R.sup.4 R.sup.3 R.sup.4
______________________________________
C.sub.3 H.sub.7 --
--C.sub.2 H.sub.5
C.sub.5 H.sub.11 --
--C.sub.5 H.sub.11
" --C.sub.3 H.sub.7
" --C.sub.6 H.sub.13
" --C.sub.4 H.sub.9
" --C.sub.7 H.sub.15
" .sup. --C.sub.5 H.sub.11
C.sub.7 H.sub.15 --
--C.sub.2 H.sub.5
" .sup. --C.sub.6 H.sub.13
" --C.sub.3 H.sub.7
" .sup. --C.sub.7 H.sub.15
" --C.sub.4 H.sub.9
.sup. C.sub.5 H.sub.11 --
--C.sub.2 H.sub.5
" --C.sub.5 H.sub.11
" --C.sub.3 H.sub.7
" --C.sub.6 H.sub.13
" --C.sub.4 H.sub.9
" --C.sub.7 H.sub.15
______________________________________
As described above, the present invention consists in that the compound
expressed by the formula (A) and having a negative dielectric anisotropy
value is contained in ferroelectric liquid crystal compositions, and
particularly when component A expressed by the general formula (A),
component B expressed by the formulas (B-1) to (B-4) and component C
expressed by the formulas (C-1) to (C-4) are combined together, then a
ferroelectric liquid crystal composition having an even larger negative
dielectric anisotropy value larger and yet having high-speed response
properties is obtained.
As described above, the achiral compound as component A has a negative
dielectric anisotropy value as large as -20 to -25 and plays an important
role in the ferroelectric liquid crystal composition of the present
invention in that it develops a negative large dielectric anisotropy value
and exhibits AC stabilizing effect and as a result, generates good memory
properties. Component A exhibits no SC phase and when it is used in a too
high concentration, the upper limit temperature of SC* phase in the
ferroelectric liquid crystal composition is lowered; hence too high a
concentration is undesirable. Thus, when the use object of component A is
taken into consideration, the concentration of component A used in the
present invention is preferably 40% by weight or less.
Compounds expressed by the formulas (B-1), (B-2), (B-3) and (B-4) as
component B are achiral compounds and play a role of basic SC compound in
the present invention.
Phenylpyrimidine compounds expressed by the formula (B-1) have SC phase
within a low temperature region. For example, in the case of a compound of
R.sup.5 =C.sub.6 H.sub.13 O- and R.sup.6 =C.sub.8 H.sub.7 - , the phase
transition points of the compound are as follows:
##STR12##
On the other hand, biphenylpyrimidine compounds expressed by the formula
(B-2) have SC phase within a high temperature region. For example, in the
case of a compound of R.sup.7 =C.sub.7 H.sub.15 - and R.sup.8 =C.sub.8
H.sub.17 - , the phase transition points are as follows:
##STR13##
In the above phase transition temperature, Cr, N and Iso represent crystal,
nematic phase and isotropic liquid, respectively.
Thus, when a compound expressed by the formula (B-1) is combined with a
compound expressed by the formula (B-2), there is obtained a basic SC
mixture having SC phase over a range from a low temperature region to a
high temperature region.
The compounds having a core of (B-1) or that of (B-2) have a superior
specific feature of a very low viscosity as already described in Japanese
patent application laid-open No. Sho 61-291,679/1986 filed by the present
inventors; hence the compounds also each play an important role as a basic
SC compound in the ferroelectric liquid crystal composition of the present
invention.
As the compound expressed by the formula (B-1), those wherein R.sup.5
represents a linear alkoxy group of 6 to 12 carbon atoms and R.sup.6
represents a linear alkyl of 8 to 11 carbon atoms and have SC phase are
particularly preferred.
On the other hand, phenylpyridine compounds expressed by the formula (B-3)
have SC phase and the like over a broad temperature range from a low
temperature region to high temperature region and, e.g. in the case of a
compound of R.sup.9 =C.sub.7 H.sub.15 - and R.sup.10 =C.sub.7 H.sub.15 - ,
the phase transition points are as follows:
##STR14##
Further, biphenyl compounds expressed by the formula (B-4) have SC phase
and the like within a low temperature region and e.g. a compound of
R.sup.11 =C.sub.7 H.sub.15 - , Z=single bond and k=3 has the following
phase transition points:
##STR15##
Compounds having a core of the general formula (B-3) or that of the formula
(B-4) have a superior specific feature as already described in EP 86108267
by the present inventors and also have a very low viscosity similar to
those of the above-mentioned pyrimidine compounds; hence the compounds
also play a role as a basic SC compound in the ferroelectric liquid
crystal composition of the present invention and are used for adjusting
tee SC phase temperature range, if necessary.
As the phenylpyridine compounds expressed by the formula (B-3), those
wherein R.sup.9 represents an alkyl group of 4 to 10 carbon atoms and
R.sup.10 represents an alkoxy group of 4 to 12 carbon atoms are
particularly preferred. Further, as the biphenyl compounds expressed by
the formula (B-4), those wherein R.sup.11 represents an alkoxy group of 7
to 10 carbon atoms, Z represents a single bond and k represents 3 and
having SC phase are particularly preferred.
As the pyrimidine compounds of the formula (B-1) or (B-2) used as a
component of the ferroelectric liquid crystal composition of the present
invention, those having SC phase are preferred as described, but even
those exhibiting no SC phase may also be used if the quantity thereof is
within a range where the SC phase temperature range of smectic
compositions to be obtained is not notably narrowed.
This applies to phenylpyridine compounds expressed by the formula (B-3) or
biphenyl compounds expressed by the formula (B-4), each exhibiting no SC
phase, and these compounds may be used for viscosity reduction or
adjustment of SC phase temperature range.
When it is taken into consideration that the use object of the compound of
component B is to use it as a base SC compound, the concentration of
component B used in the present invention is preferably 70% by weight or
less.
Compounds of component C expressed by the formulas (C-1), (C-2), (C-3) or
(C-4) are chiral compounds, and a patent application for compounds
expressed by the formulas (C-1) or (C-2), which has been laid open, has
already been applied for by the present applicants and (e.g. Japanese
patent application laid-open Nos. Sho 61-43/1986, Sho 61-210056/1986 and
Sho 63-48254/1988). The compounds exhibit SC* phase within a high
temperature region, have a large tilt angle and a very large spontaneous
polarization value. For example, a compound of the formula (C-1) wherein
R.sup.12 =C.sub.8 H.sub.17 O- , R.sup.13 =-C.sub.6 H.sub.13 and W=-F has
the following phase transition points:
##STR16##
and a tilt angle of 34.5.degree. and a Ps of
132 nC/cm.sup.2 (T-Tc=-30.degree. C.).
A compound of the formula (C-1) wherein R.sup.12 =C.sub.6 H.sub.13 O- ,
R.sup.13 =-C.sub.6 H.sub.13 and W=-H has the following phase transition
temperatures:
##STR17##
and a tilt angle of 38.1.degree. and a Ps of
110 nC/cm.sup.2 (T-Tc=-30.degree. C.).
A compound of the formula (C-1) wherein R.sup.12 =C.sub.8 H.sub.17
O-R.sup.13 =C.sub.6 H.sub.13 and W=-CN has the following phase transition
points:
##STR18##
and a tilt angle of 25.degree. and a Ps of
240 nC/cm .sup.2 (T-Tc=-30.degree. C.).
Further a compound of the formula (C-2) wherein R.sup.14 =C.sub.8 H.sub.17
O- , R.sup.15 =-C.sub.6 H.sub.13 and V=-F has the following phase
transition points:
##STR19##
and a tilt angle of 36.5.degree. and a Ps of
109 nC/cm.sup.2 (T-Tc=-30.degree. C.).
A compound of the formula (C-2) wherein R.sup.14 =C.sub.8 H.sub.17 O- ,
R.sup.15 =-C.sub.6 H.sub.13 and V=-H has the following phase transition
points:
##STR20##
and a tilt angle of 45.degree. and a Ps of
39 nC/cm.sup.2 (T-Tc=-30.degree. C.).
A compound of the formula (C-2) wherein R.sup.14 =C.sub.8 H.sub.17 - ,
R.sup.15 =-C.sub.6 H.sub.13 and V=-CN have the following phase transition
points:
##STR21##
and a tilt angle of 22.degree. and a Ps of
137 nC/cm.sup.2 (T-Tc=-15.degree. C.).
Thus, the compounds of the formulas (C-1) or (C-2) play important roles of
development of high-speed response properties, improvement in the tilt
angle and improvement in the upper limit temperature of SC* phase in the
ferroelectric liquid crystal composition of in the present invention.
On the other hand, a patent application, not yet laid open, for the
compounds expressed by the formulas (C-3) or (C-4) has already been
applied for by the present inventors and (e.g. Japanese patent application
Nos. Sho 61-133269/1986, Sho 62-049796/1987, etc.). The compounds have a
very large spontaneous polarization value (extrapolated value: about 100
nC/cm.sup.2) and far superior response properties. Thus, the compounds
play an important role of development of high-speed response properties in
the ferroelectric liquid crystal composition of the present invention.
When the concentration of components A and B used and also the utility of
component C are taken into consideration, the concentration of component C
used in the present invention is preferably 40% by weight or less.
The respective proportions of components A, B and C having made use of the
above-mentioned specific features of these components to obtain the
objective liquid crystal composition having superior specific features
have been variously examined, and as a result, it has been found that a
concentration of component A in the range of 5 to 40% by weight, that of
component B in the range of 20 to 70% by weight and that of component C in
the range of 5 to 40% by weight as described above are preferred.
The present invention will be described in more detail by way of Examples,
but it should not be construed to be limited thereto.
In the Examples, the spontaneous polarization value (Ps) was measured
according to Sawyer-Tower method; the helical pitch (P) was sought by
directly measuring the distance between the dechiralization lines
corresponding to the helical pitch under a polarizing microscope; and the
tilt angle (.theta.) was sought from the moved angle (corresponding to
2.theta.) of the extinction site under crossed nicols by impressing an
electric field sufficiently higher than the critical one upon the
homogeneously aligned cell to extinguish the helical structure and further
inverting the polarity.
The response time was measured from the change in the intensity of
transmitted light observed when the respective compositions were filled in
a cell subjected to an aligning treatment and having a distance between
the electrodes of 2 .mu.m and a square wave having a V.sub.pp (Voltage of
peak to peak) of 20 V and 100 Hz was impressed.
The dielectric anisotropy value was calculated by using a cell subjected to
a parallel aligning treatment and a vertical aligning treatment and
measuring the dielectric constant from the capacity of the empty cell and
the capacity in the case where a liquid crystal was filled therein.
EXAMPLE 1
A ferroelectric liquid crystal composition D composed mainly of components
B and C used in the present invention and having the following proportions
of the components was prepared:
__________________________________________________________________________
Composition D
__________________________________________________________________________
##STR22## 17.5
wt. %
##STR23## 5 wt. %
##STR24## 10 wt. %
##STR25## 10 wt. %
##STR26## 7.5
wt. %
##STR27## 20 wt. %
##STR28## 15 wt. %
##STR29## 10 wt. %
##STR30## 5 wt. %
__________________________________________________________________________
This ferroelectric liquid crystal composition D exhibited SC* phase within
a temperature region of -21.degree. to +56.degree. C., exhibited SA phase
on the higher temperature side thereof, formed N* phase at 68.degree. C.
and formed isotropic liquid at 73.degree. C. At 25.degree. C., it had a
spontaneous polarization value of 8.5 nC/cm.sup.2, a tilt angle of
25.degree. and a response time of 15 .mu.sec (electrolytic intensity:
E=.+-.0.5 V/.mu.m). Further, its dielectric anisotropy value was +0.5.
This composition D was filled in a cell provided with two substrates
having transparent electrodes each surface of which was subjected to
rubbing treatment and having a cell thickness of 5 .mu.m to prepare an
electrooptical element. This element was placed between two crossed
polarizers and a pulse wave (pulse width: 600 .mu.sec and wave height
value: 25 V) as shown in FIG. 1(a) was impressed. As a result, no memory
properties were observed (see FIG. 1(b)). Thus, an AC wave of 20 KHz and
25 V was overlapped with the above pulse wave to observe change in the
level of transmitted light. As a result, no memory properties were
similarly observed and change in the intensity of transmitted light as
shown in FIG. 1(b) was observed. Thus, to the composition D was added the
following achiral compound as component D of the present invention having
a negative dielectric anisotropy value to prepare a ferroelectric liquid
crystal composition E:
##STR31##
This ferroelectric liquid crystal composition E exhibited SC* phase within
a temperature region of -22.degree. to +53.degree. C., exhibited SA phase
on the higher temperature side, formed N* phase at 60.degree. C. and
formed isotropic liquid at 69.degree. C. At 25.degree. C., it had a
spontaneous polarization value of 7.5 nC/cm.sup.2, a tilt angle of
22.degree. and a response time of 230 .mu.sec (E=.+-.5 V/.mu.m). Further,
its dielectric anisotropy value was -2.
This composition E was filled in a cell similar to that in the case of the
composition D, followed by impressing a pulse wave shown in FIG. 1(a). As
a result, no memory properties were observed as in the case of composition
D (see FIG. 1(b)). Whereas, when an AC wave of 20 KHz and 25 V was
overlapped with the wave shown in FIG. 1(a), good memory properties as
shown in FIG. 1(c) were observed. This fact may be interpreted as follows:
when the compound having a negative dielectric anisotropy value as
component A of the present invention was added, the resulting
ferroelectric liquid crystal composition had a negative larger dielectric
anisotropy value, and as a result, AC stabilizing effect was notably
developed to afford superior memory properties. The response time was
shorter (about 1/4 ) and yet AC voltage was lower (about 1/2) as compared
with the results of the report of Jeary; hence it has been found that the
ferroelectric liquid crystal composition of the present invention is very
practical.
EXAMPLES 2-7
The proportions of the ferroelectric liquid crystal compositions Nos. 1-6
of the present invention are shown in Table 3 and the specific features
thereof are shown in Table 4. In addition, the respective proportions in
Table 3 all refer to percentage by weight.
TABLE 3
__________________________________________________________________________
Composition No. and
proportions
(% by weight)
Component
Formula
Compounds 1 2 3 4 5 6
__________________________________________________________________________
A A
##STR32## 5 5 5
A
##STR33## 5 5 5
A
##STR34## 5
A
##STR35## 5
A
##STR36## 5 5
A
##STR37## 5 5 5 5 5 5
A
##STR38## 5 5 5 5 5
B B-1
##STR39## 12.4
12.2
5 4.4
4.1
3.6
B-1
##STR40## 8.6
8
B-1
##STR41## 4.3
4.1
B-1
##STR42## 4.3
4.1
B-2
##STR43## 8.6
8
B-2
##STR44## 4.3
4.1
B-2
##STR45## 5 4.4
4.1
3.6
B-2
##STR46## 5 4.4
4.1
3.6
B-2
##STR47## 5 4.4
4.1
3.6
B-2
##STR48## 5 4.4
4.1
3.6
B-3
##STR49## 5 4.4
4.1
3.6
B-3
##STR50## 5 4.4
4.1
3.6
B-3
##STR51## 5 4.4
4.1
3.6
B-3
##STR52## 5 4.4
4.1
3.6
B-3
##STR53## 5 4.4
4.1
3.6
B-4
##STR54## 14.3
13.5
C C-1
##STR55## 14.3
13.5
4.5
4 3.8
3.3
C-1
##STR56## 9 8 7.5
6.5
C-1
##STR57## 4.5
4 3.8
3.1
C-3
##STR58## 9 4 7.5
6.5
C-4
##STR59## 4
Others
##STR60## 4.8
4.5
##STR61## 4.8
4.5
##STR62## 4.8
4.5
##STR63## 9.5
9
##STR64## 9 8 7.5
6.5
##STR65## 4 4 3.9
3.1
__________________________________________________________________________
TABLE 4
__________________________________________________________________________
Composition No.
Characteristics
1 2 3 4 5 6
__________________________________________________________________________
Phase transition
point (.degree.C.)
Cr .fwdarw. SC*
-18 -19 -24 -36 -35 -28
SC* .fwdarw. SA
63 66 65 59 62 49
SA .fwdarw. N*
68 68 74 69 68 64
N* .fwdarw. Iso
81 84 81 80 82 77
Spontaneous (nC/cm)*
6 6 15 16 16 7
polarization value
Tilt angle (.degree.)*
22 21 21 23 23 17
Helical (.mu.m)*
2 2 4 3 3 2
pitch
Response (.mu.sec)*
275 563 130 400 430 675
time
Dielectric* -2 -3 -4 -5 -7 -9
anisotropy
__________________________________________________________________________
*Values at 25.degree. C.
In addition, Table 3 also includes compositions containing chiral compounds
having the objective of elongating the helical pitch of SC* phase or
broadening the temperature region of SC* phase, but it does not damage the
specific features of the ferroelectric liquid crystal composition of the
present invention to contain such chiral substances in the composition,
which therefore raise no problem.
A ferroelectric liquid crystsl composition No. 3 of the present invention
was filled in a cell provided with transparent electrodes each obtained by
coating PVA as an aligning agent and rubbing the resulting surface to
subject it to a parallel aligning treatment and having a cell gap of 5
.mu.m, followed by placing the resulting liquid crystal cell between two
polarizers arranged at crossed nicol state and causing a pulse wave having
a pulse width of 400 .mu.sec and a wave height value of 25 V to overlap
with an AC wave of 20 KHz and 20 V. As a result, a good AS stabilizing
effect was observed to obtain a liquid crystal display element having good
memory properties and also a contrast ratio as very good as 1:20.
According to the present invention, a ferroelectric liquid crystal
composition which makes the negative spontaneous polarization value
larger, has AC stabilizing effect and yet has high-speed response
properties, and a light switching element using the above composition are
obtained. As the use applications of the ferroelectric liquid crystal
composition of the present invention, a high-speed shutter, a
high-multiplex liquid crystal display, etc. are exemplified.
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